The present invention relates to an arrangement and a method for recirculation of exhaust gases of a combustion engine and controlling temperature of exhaust gases recirculated.
The technique called EGR (Exhaust Gas Recirculation) is a known way of leading part of the exhaust gases from a combustion process in a combustion engine back, via a return line, to an inlet line for supply of air to the combustion engine. A mixture of air and exhaust gases is thus supplied via the inlet line to the engine's combustion spaces. Adding exhaust gases to the air causes a lower combustion temperature resulting inter alia in a reduced content of nitrogen oxides NOx in the exhaust gases. This technique is used for both Otto engines and diesel engines.
The return line for exhaust gases usually comprises components such as an EGR valve which regulates the exhaust flow through the return line, and an EGR cooler for cooling the recirculating exhaust gases. An electronic control system controls the EGR valve so that a specified amount of exhaust gases is returned and is mixed with the air in the inlet line to the combustion engine. The result is a substantially optimum combustion process in the combustion engine while at the same time the formation of emissions is substantially minimised. The coolant of the combustion engine's cooling system is in many cases used for cooling the returning exhaust gases in the EGR cooler. The coolant in the combustion engine's cooling system is also commonly used for heating cab spaces in the vehicle. The coolant of a vehicle thus has a plurality of functions. For these functions to work well it is necessary that the temperature of the coolant be within a specific range, which may be 80° C.-100° C.
Conventional cooling systems usually comprise a thermostat which prevents the coolant being led to the radiator when it is at too low a temperature. Relatively rapid heating of the coolant in cooling system is thus made possible, but still more rapid heating of the radiator fluid in the cooling system would be desirable, particularly when there is a cold ambient temperature, in order to reduce the time during which cold coolant is led through the combustion engine. Leading cold coolant through the combustion engine results in excessive cooling of the combustion engine, which may inter alia lead to bad engine function, greater engine noise, increased discharge of emissions and shorter service life of the combustion engine. When there is a cold ambient temperature, more rapid heating of the coolant is also desirable to enable quicker heating of the vehicle's cab space. With a conventional arrangement it may also be difficult to maintain the temperature of the coolant when there is a cold ambient temperature and during operating periods when the combustion engine is running at low load.